In conventional propulsion systems, propellers perform the work required to accelerate fluid molecules to a desired velocity, but the propellers are unable to operate further on the fluid molecules to follow up on the work that was expended to overcome the initial inertia. This is due to the fact that a fluid molecule at rest tends to remain at rest and thus once placed in motion, a relatively smaller amount of energy is required to further accelerate it. Additionally, parts in conventional propulsion systems are easily damaged by foreign objects and unprotected screw-type propulsion systems pose a danger to divers and other living systems which pass in the vicinity of the propulsion system.
Those skilled in the art relating to propulsion systems have found that the propulsion efficiency of a propeller may be increased by carefully channeling the fluid flow to a propeller and similarly directing the accelerated fluid flow efficiently as it leaves the back of the propeller. In the past, various types of conical enclosures or nozzles have been fashioned in an attempt to increase the performance of propellers.
Essentially, a conical enclosure or nozzle surrounds the propeller in a longitudinal direction and directs fluid flow exiting from the propeller blades. The principles of fluid dynamics dictate that the volume of water flowing into the propeller will equal the volume of water flowing out. As such, the diameter of the nozzle is reduced as the water flows rearward and out of the nozzle. Since the volume of water exiting must equal the volume that enters the nozzle, the water flow accelerates as it travels through the nozzle and thereby provides additional thrust which cannot be achieved by the propeller alone.